Sepp Blatter rocked the world of soccer on Tuesday by unexpectedly saying he would step down as FIFA president in the wake of a corruption investigation that reportedly may include the embattled chief himself.

Citing sources familiar with the case, The New York Times and ABC News reported on Tuesday that Blatter was being investigated by the Federal Bureau of Investigation and U.S. prosecutors. Reuters was not immediately able to confirm the report. Blatter has not been charged with any wrongdoing.

Blatter, 79, announced his decision to step down at a hastily arranged news conference in Zurich, six days after police raided a hotel in the city and arrested several FIFA officials, and four days after he was re-elected to a fifth term as FIFA president.

Blatter said an election to choose a new president would be held as soon as possible, though a FIFA official said it would probably not take place until at least December.

"FIFA needs profound restructuring," said Blatter, a Swiss national who has been a dominant presence at FIFA for decades.

"I decided to stand again to be elected because I was convinced it was the best option for football.

"Although the members of FIFA gave me a new mandate, this mandate does not seem to be supported by everyone in the world."

Blatter's decision to step down as the growing scandal plunges FIFA further into the worst crisis in its history was welcomed by his most prominent critics.

European football federation chief Michel Platini, a French former international player and favorite to succeed Blatter as FIFA president, said: "It was a difficult decision, a brave decision, and the right decision."

The second favorite on the list, Jordan's Prince Ali bin Al Hussein, who stood against Blatter but withdrew after gaining 73 votes to Blatter's 133 in the first round of last Friday's vote, stopped short of confirming that he would run again.

Asked if there should be a fresh start at FIFA, he told Britain's Channel 4 News, "I'm willing to help."

Greg Dyke, chairman of the English Football Association and one of Blatter's most outspoken critics, said it was "good news for world football" but then questioned Blatter's motive. "Who got him? Who shot him?" he asked.

"I don't believe he went for any sort of moral basis so something has happened between then and now which means he has to resign."

FIFA, which Blatter had led since 1998, was shocked last week by the announcement of a U.S. investigation into alleged widespread financial wrongdoing stretching back more than two decades.

Swiss authorities also mounted their own criminal probe into the awarding of the 2018 and 2022 World Cups to Russia and Qatar, respectively.

Russian Sports Minister Vitaly Mutko said Blatter's decision to step down was "courageous" and would help prevent a split in FIFA.

While Blatter was not mentioned in the U.S. or Swiss investigations, there had been widespread calls for him to quit, mostly from Western nations. Some major sponsors also expressed misgivings about the impact of the scandal.

"Today's news marks a step in the right direction on FIFA's path to establish and follow transparent compliance standards in everything they do," Adidas said.

The U.S. Justice Department, the FBI and the U.S. Attorney's office had no immediate comment.

The office of the Swiss Attorney General, which is investigating alleged criminal mismanagement and money laundering at FIFA, said Blatter's resignation would have no effect on its proceedings. It said Blatter himself was not subject to investigation.

Blatter is only the eighth man to hold the office of president since FIFA was formed 111 years ago. Besides Platini and Prince Ali, several other candidates may emerge in the election for a new president, including Domenico Scala, independent chairman of the audit and compliance committee of FIFA.

Scandal intensifies

European sports officials said it was an important move but that FIFA needed deeper changes. French Sports State Secretary Thierry Braillard called it a first step to restore confidence. "Beyond the people, structural reforms must be undertaken."

Blatter had initially attempted to bat away the furore, relying on his extensive network of friends to hold on to power at FIFA.

Football associations in Africa and Asia had stood by him despite the scandal, saying they welcomed the FIFA funds he channeled to them for the development of the game in impoverished parts of the world.

Kalusha Bwalya, Football Association of Zambia president and former African Footballer of the Year, said he was shocked. "The man has done a lot for FIFA," he said. "For Africa he was always there, he was always caring."

The investigation closed in on Blatter on Tuesday, when FIFA denied that his right-hand man, Secretary-General Jerome Valcke, was implicated in a $10 million payment relating to the 2010 World Cup in South Africa that is at the heart of the U.S. case.

At the same time, a letter addressed to Valcke from the South African Football Association was published outlining the transaction.

Hours later FIFA called the emergency news conference and Blatter, who became FIFA secretary general in 1981 and president 17 years later, announced his decision.

During his FIFA career he survived a series of scandals including widespread accusations that Qatar bought the right to stage the 2022 World Cup in a country with little football history and where summer temperatures regularly top 40 degrees Celsius (104 F). Qatar has always denied any wrongdoing.

After what was described as the worst day in FIFA's history last Wednesday, Blatter told the conference: "Football needs a strong and experienced leader. One that knows all the ins and outs and can work with our partners".

Overcoming opposition from European soccer's governing body UEFA, which threatened at one point to boycott the Congress, he was elected for another four years. He was just days into his fifth term before deciding to step down.